We have dissociated myocardial muscle cells from adult rats and rabbits. These preparations are being used to study the contractile, electrophysiological, and biochemical characteristics in a variety of different conditions. In particular we have been able to identify in these isolated cells a longitudinally propagating wave which occurs spontaneously in cells with a normal resting membrane potential which are not electrically stimulated. These "waves" are likely to represent the phenomenon of spontaneous release of calcium from the sarcoplasmic reticulum (SR) and are the cause of the scattered light intensity fluctuations (SLIF) which our laboratory has studied in the past in multicellular preparations. With our work we have initially validated single cells as a model for the study of mechanisms of excitation-contraction coupling and in particular of spontaneous SR calcium release. We have recently expanded our work to study the interaction between spontaneous contractile waves and stimulated twitches.